A cost-effective process that combines electrospinning and a galvanic displacement reaction was utilized to synthesize ultralong hollow PbxSeyNiz nanofibers with controlled dimensions, morphology, composition, and crystal structure. Ni nanofibers were electrospun with an average diameter of 150 nm and were used as the sacrificial material for the galvanic displacement reaction. The composition and morphology of the PbxSeyNiz nanofibers were controlled during the reaction by tuning the concentration of HSeO2+ in the electrolytes. Hollow PbxSeyNiz nanofibers with smooth surfaces were obtained from the low-concentration HSeO2+ solution (i.e., 0.01 and 0.05 mM), but the hollow nanofibers synthesized from the high-concentration HSeO2+ solution (i.e., 1 mM) have rough outer surfaces with nanocrystal protrusions. The Pb content of the nanofibers' composition was varied from 3 to 42% by adjusting the HSeO2+ concentration. The thermoelectric properties of the nanofiber mats were characterized, and the highest Seebeck coefficient of approximately 449 mu V/K at 300 K was found for the Pb37Se59Ni4 nanofiber mat.